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Effect of soil-applied protoporphyrinogen oxidase inhibitor herbicides on root rot severity of soilborne pathogens in soybean [Glycine max (L.) merr.]

Nicholas Arneson: University of Nebraska-Lincoln

<div>Injury to soybean seedlings can allow infection by pathogens such as <em>Fusarium</em> spp., <em>Rhizoctonia solani</em>, and <em>Pythium</em> spp. Soil-applied protoporphyrinogen oxidase inhibitor herbicides (PPOs) can result in injury under certain environmental conditions during crop emergence. Use of PPOs in soybean production is common in integrated weed management, thus there is a need to understand the relationship between PPO injury and seedling disease. In 2017, a study was replicated at five Nebraska field sites, using a randomized complete block design with 2✕3✕2 factorial of two cultivars (sensitive and tolerant to sulfentrazone), three herbicides (glyphosate [GLY], sulfentrazone + GLY, and flumioxazin + GLY), and two seed treatments (ST; with and without fungicide). The objectives were to determine the effects of soil-applied PPOs on root rot and of fungicide ST on root rot when PPOs are used. Seedlings were collected and root rot disease severity measured. At Lincoln, flumioxazin resulted in 6% increase in root rot severity in the tolerant cultivar compared to GLY (P<0.01) and sulfentrazone had a 4% decrease in the sensitive cultivar compared to GLY (P<0.01). However, at Mead, sulfentrazone with no ST had 10% less root rot severity (<em>P</em><0.05). Effects on soybean root rot in Nebraska varied by location with PPO use, yet yield impact was not clear. As PPOs continue to be used, more studies under variable disease pressure and environments are needed to understand this interaction.</div>